The present invention relates to a portable fuel cell stack which can be used in various applications, such as a power source for outdoor activities and picnics and a household generator, and which uses light, silent and pollution-free solid polymer cells.
Fuel cell stacks generally use hydrogen as a main fuel and take out the energy generated during the chemical reaction of this hydrogen with oxygen. There are several types of fuel cell stack and one type is a solid polymer electrolyte fuel cell stack. This solid polymer electrolyte fuel cell stack has features such as low operating temperature and high output density.
An example of fuel cell stack in which such conventional solid polymer electrolyte fuel cell stack is disclosed in U.S. Pat. No. 5,595,834. As shown in FIG. 5, a unit cell 10 comprises a solid polymer electrolyte membrane 12, an anode (fuel electrode) 13a and a cathode (oxygen electrode) 13b, which are provided on both sides of the solid polymer electrolyte membrane 12, a fuel flow field plate 14 and an oxygen flow field plate 18, which are provided on sides of these electrodes 13a and 13b, and separator plates 34, which are provided on sides of these flow field plates 14 and 18, to form the unit cell 10 by making them integral with each other. A plurality of unit cells 10 are stacked, and the stacked unit cells 10 are formed as a whole construction by inserting a fuel distribution manifold, which comprises a hydrophilic sleeve 32 connected to the fuel flow field plate 14, into a center hole of the unit cell 10, by further providing end plates 24 on both ends of a bolt 26, which is passed through the center of the sleeve 32, so as to sandwich them between the two ends of the bolt 26, and by fastening and fixing the whole by means of nuts via washers 38a to 38d and an O-rings 36. Because such fuel cell stacks are suitable for low power fuel cells, they can be designed as small-sized and lightweight fuel cell stacks.
Furthermore, in this polymer electrolyte fuel cell stack, a fuel feed flow field plate 29 is provided between one end plate 24 and the separator plate 34 adjacent to the unit cell 10 to provide communication with the hydrophilic sleeve 32, which constitutes the fuel distribution manifold for supplying fuel to the fuel flow field plate 14, and a port 28 is provided in the outer peripheral portion of the end plate 24 so that fuel is introduced into the port 28 and supplied to the fuel flow field plate 14.
However, in the above conventional electrolyte fuel cell stack, because the two electrodes of anode (fuel electrode) 13a and cathode (oxygen electrode) 13b are provided on both surfaces of the solid polymer electrolyte membrane 12 and the fuel flow field plate 14 and oxygen flow field plate 18 are provided on sides of these electrodes 13a and 13b, there are many contact portions, with the result that internal resistance is large and that the performance of the whole cell stack decreases.
Moreover, the above conventional electrolyte fuel cell stack not only has a large number of components, such as the fuel flow field plate 14 and fuel feed flow field plate 29 on the fuel supply side and the port 28 of the end plate 24 for fuel supply, but also is of a construction that fuel is fed from the side of the end plate 24 toward the center via the fuel feed flow field plate 29, resulting in an increase both in the flow resistance of the fuel supply passage and in the concentration fluctuation of fuel, thus having an influence on stable energy supply. Using a large number of components causes burdensome maintenance, complex shape and large size.
The present invention was made in view of the foregoing problems. Accordingly, an object of the invention is to provide a portable fuel cell stack in which the number of components is reduced by reducing the number of flow field plates, cell stack performance is improved by reducing the number of contact portions to thereby lower internal resistance, fuel is fed and supplied from the center of an end plate directly to a fuel distribution manifold.
Another object of the invention is to provide a portable fuel cell stack which is capable of being further reduced in size and weight by reducing the number of components.
In the first concept of the invention for achieving the above objects, a unit cell is provided in an electrolytic fuel cell stack, which includes a polymer electrolyte membrane, an oxygen electrode and a fuel electrode provided on both sides of the polymer electrolyte membrane, a flow field plate installed on the oxygen electrode side, a separator plate installed on the outside of the flow field plate on the oxygen electrode side so as to be in contact therewith, and another separator plate installed on the outside of the fuel electrode so as to be in contact therewith.
According to this first concept, the following advantageous effects are obtained:
(1) Because the flow field plate installed on the fuel electrode side in the conventional electrolyte fuel cell stack is not provided, the number of contact surfaces decreases by two surfaces and the electric resistance in the contact portions decreases so as to lead to a decrease in internal resistance and make it possible to perform the energy generation of the cell stack efficiently.
(2) Because the number of parts of a unit cell decreases, it is possible to make an inexpensive product as a whole and the assembling of unit cells becomes easy, making it possible to increase the production efficiency.
The second concept of the invention is characterized in that one of the fixing nuts has a fuel supply port which provide communication with the fuel distribution manifold for fuel supply from the center of the end plate.
By this second concept, the following effects are obtained:
(3) Because the fuel is directly supplied to the fuel distribution manifold without flowing through the fuel flow field, the flow resistance decreases and fuel supply can be smoothly performed. In addition, the concentration fluctuation in fuel supply can be reduced. Therefore, stable power generation can be carried out.
(4) Because the fuel flow field in the cell stack was eliminated, the number of components of the cell stack can be reduced and besides the cell stack can be reduced in size and weight.
Furthermore, by the third concept of the invention, the fuel distribution manifold is formed by arranging hydrophilic synthetic fiber threads on a tie bolt in the axial direction of the tie bolt.
(5) Because this fuel distribution manifold by the third concept uses hydrophilic synthetic fibers, it is possible to select a material for the fuel distribution manifold from easily obtainable ones and the fuel distribution manifold can be easily formed because of low cost and easy handling.
In addition, according to the fourth concept of the invention, the other fixing nut is provided with a bleeder valve capable of supplying fuel to the flow field plate, etc. by one-touch operation at the end of the bolt.
(6) Because the other fixing nut according to the fourth concept is provided with a bleeder valve, during the startup of the fuel cell stack, fuel can be supplied in a sufficient amount by one-touch operation to the fuel electrode side of the polymer electrolyte membrane, whereby the power generation action during startup can be smoothly started.